Effects Of N Addition On Plant Diversity In A Typical Mixed Broadleaved-Korean Pine Forest

In recent decades,the temperate forest ecosystems experienced serious negative effects due to atmospheric nitrogen(N)deposition problem which caused by the rapid development of industry,agriculture,animal husbandry and human activities.The forest biodiversity also suffered a serious threaten because of this.As an important factor in maintaining forest ecosystem balance,Forest biodiversity is great importance.We examined the effects of experimental N addition on plant diversity in a mixed typical mixed broadleaved-Korean pine forest in Xiaoxing’an Mountains.Experimental N additions were administered at the following levels since 2008:NO(0 kg N hm-2yr-1),N1(30 kg N hm-2 yr-1),N2(60 kg N hm-2yr-1)and N3(120 kg N hm-2 yr-1).Additionally,plant diversity was studied from 2014 to 2016.The results are as follows.Nitrogen treatment significantly changed the soil properties.The total N and available P in soil were greater with elevated N treatment levels.And the soil pH value decreased with the increasing level of N addition.Under different N treatment,the species numbers and average height of different functional groups showed different changing trends and obvious seasonal difference.In summer,the average height of herbaceous community increased with the increasing level of N addition.The other functional group showed no obvious differences.But some species.such as tree seedlings and ferns,never appeared in N3.And the species numbers and average height of different species showed different changing trends and obvious seasonal difference.N treatment,Seasons and Year had different effect on the species richness of four functional groups.The N treatment significantly affected species richness of four functional groups,but different N treatment has different influence on the species richness of each functional group and obviously seasonal variation.High-N treatment significantly decreased species richness of four functional groups.Different N treatment showed different influence of the cover and density of four functional groups.From spring to autumn at 2016,the density and cover of herbaceous community showed upgrade firstly than descending latter tendency,while the other three functional groups showed a decreasing trend.The conclusion is that the long-term high-N addition ultimately reduced plant diversity by changing the soil nutrient contents,decreasing the pH values,and changing the community species composition and structure.